Two CDROM drives, Apple scsi 8x & 12x,
Matsushita CR8008 v. 8.0e, Matsushita CR8012 v.1.0g

Both work fine, read most any disk I give them,
if they are connected to:
LC3 OS 7.1 QT 2.5
6100 OS 8.1 QT 2.5
7200/120 OS 9.1 QT 4.12
7300/180 OS 8.1 QT 4.1
7600/200 OS 9.2 QT 5.02

They will read old DOS CDs, and play mpeg1 or 2 VCDs

Trouble comes if I attempt to upgrade the 6100 or 7300 to OS 9.1,
then they will read only Macintosh formatted data disks.
Put in any other format and the dialog appears:

This disk is unreadable by this Macintosh
Do you wish to initialize it?

I've tried swapping round the driver extensions,
checked the QuickTime installs, even combed thru
the System files with ResEdit. nada...

any clues?